I was playing with an EIGRP Lab in GNS3, and came across a very weird oddity.
Here is the topology:
Here is the oddity:
R2# show ip eigrp topology
<~-~-~ output ommitted ~-~-~>
P 10.4.5.0/24, 1 successors, FD is 309760 <----
via 10.2.3.3 (332800/307200), FastEthernet0/0
P 10.3.4.0/24, 1 successors, FD is 307200
via 10.2.3.3 (307200/281600), FastEthernet0/0
Notice for 10.4.5.0/24, I am seeing two different values displayed for Feasible Distance. The line with the arrow reports the FD as 309760
. The line just below it reports the FD as 332800
.
I included the route for 10.3.4.0/24 as a comparison, In that route (as I expect it to be), the FD in the first line matches the FD in the second line (both 307200
).
Looking at the EIGRP route in more detail:
R2# show ip eigrp topology 10.4.5.0/24
IP-EIGRP (AS 99): Topology entry for 10.4.5.0/24
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 309760
Routing Descriptor Blocks:
10.2.3.3 (FastEthernet0/0), from 10.2.3.3, Send flag is 0x0
Composite metric is (332800/307200), Route is Internal
Vector metric:
Minimum bandwidth is 10000 Kbit <----
Total delay is 3000 microseconds <----
Reliability is 255/255
Load is 1/255
Minimum MTU is 1500
Hop count is 2
We can use the highlighted values to calculate the EIGRP Metric using the default K-values and this formula: 256 * (BW + Delay). Which equates to:
256 * (1000 + 300) = 332800
So the Feasible distance to 10.4.5.0/24 on R2 is 332800. And the show ip route
output is indeed showing this:
R2# show ip route 10.4.5.0
Routing entry for 10.4.5.0/24
Known via "eigrp 99", distance 90, metric 332800, type internal
But for whatever reason, in the EIGRP topology table, I am seeing this other strange value 309760
:
R2# show ip eigrp topology
P 10.4.5.0/24, 1 successors, FD is 309760
via 10.2.3.3 (332800/307200), FastEthernet0/0
What is causing the 309760 value? Why am I seeing two different values in what I thought was always the Feasible Distance? Why is the 10.4.5.0/24 route the only one in my network that is showing two different values?